The parasite that causes malaria invades and prospers in various tissues such as skin, blood, liver, gut, and salivary glands of its human and mosquito hosts. The invasion of many different kinds of cells implies that the parasite makes use of a diverse cell biology of receptor-ligand interactions. By determining the three-dimensional structures of receptor and ligand proteins, we are studying the interactions that allow the parasite to specifically target a particular type of cell to invade. The parasite receptors, being on the cell surface, are also prime candidates for the development of anti-malarial vaccines as immunity to malaria appears to correlate with immune responses to cell surface receptors. We have crystallized two malarial proteins and are actively working on several more. With x-ray diffraction data in hand for one receptor, we are proceeding to determine its structure and are obtaining x-ray data on a second receptor. We hope through these studies to reveal the overall shapes and the specific interactions of important receptors on the parasite.